Generally, a swash plate hydraulic pump is used in many fields since its outer shape is small and control for making its discharge capacity variable is easy. Particularly, in construction equipment, an industrial vehicle, or the like, a plurality of swash plate hydraulic pumps are coupled in series (hereinafter a phrase “in tandem” is used) by making the most of their merit, and thereby used as a tandem type swash plate hydraulic pump. For example, in a hydraulic shovel, a rough terrain crane, or the like of construction equipment, a plurality of swash plate hydraulic pumps are coupled in tandem for use in an operating machine, slewing, traveling, and attachment. The swash plate hydraulic pump is provided in an engine room and attached to an engine as a driving source, and discharges pressurized oil by being directly driven to operate the operating machine and the like.
Since the swash plate hydraulic pump is provided in the engine room as described above, it is demanded that the axial overall length of the swash plate hydraulic pump is short, and as its improvement example, Japanese Patent Publication No. 3-59275, Japanese Patent Laid-open No. 8-121328, Japanese Patent Laid-open No. 2001-140748, and so on are disclosed.
In all of these Patent Bulletins, two tandem type swash plate hydraulic pumps are used, a gear case is attached to an intermediate casing provided in an intermediate portion therebetween, and a hydraulic pump is additionally provided in this gear case in parallel with the tandem type swash plate hydraulic pumps. The additionally provided hydraulic pump is formed so as to be driven by meshing a gear having a shaft parallel to the hydraulic pump with the intermediate casing or the gear case, or by a chain.
In the above, for example, according to Japanese Patent Laid-open No. 8-121328, a tandem type swash plate hydraulic pump is provided with a driving force take-out mechanism for taking out driving force in a spline sleeve member of a spline joint which is an intermediate joint portion. The driving force take-out mechanism is provided with a first gear coupled to the spline sleeve member and a gear box, and the gear box is composed of an intermediate gear and a driven gear, the spline sleeve member, and a gear case for rotatably housing these components. The gear case is removably fixed to an intermediate block of the tandem type swash plate hydraulic pump, and a pump attaching portion for attaching hydraulic pumps which may be additionally provided as necessary is provided on either side of the gear case. The additionally provided hydraulic pumps are attached in parallel to the tandem type swash plate hydraulic pump.
Thus, it is disclosed that a driving force transmission system for additionally providing one or plural hydraulic pumps and a structure related to the system can be simplified and reduced in weight, and that even one or plural hydraulic pumps are additionally provided, the tandem type swash plate hydraulic pump capable of housing them compactly without increasing the axial length of a pump unit is obtained.
In recent years, in construction equipment such as a hydraulic shovel and a rough terrain crane, a revolving superstructure is made smaller relative to a base carrier, and the revolving superstructure can revolve within the width of the base carrier. As a result, an engine room attached to the revolving superstructure becomes smaller. In the engine room, a driving source including an engine, a radiator, and the like and its related components, and hydraulic equipment such as a hydraulic pump and a direction changeover valve are housed. For example, as shown in FIG. 12, components related to the driving source including an engine 80 and a radiator 81, and a hydraulic pump 83 are provided in tandem in an engine room 84. Therefore, a hydraulic pump is additionally provided as described above without increasing the axial length of the hydraulic pump 83.
Especially, in a small-sized hydraulic shovel, the proportion of the outer shape of a revolving superstructure 87 is high relative to the crawler width of a carrier 86, and the proportion of a plane area of a driver's cab 88 to the revolving superstructure 87 is high. Accordingly, in the small-sized vehicle, in order to downsize the engine room 84, the downsizing of the engine 80 and the hydraulic pump 83 is demanded. In a large-sized vehicle, in order to drive an operating machine, a hydraulic pump with a large discharge quantity is required, and since the attachment of a plurality of hydraulic pumps becomes necessary, the downsizing of the engine 80 and the hydraulic pump 83 is demanded similarly to the small-sized vehicle.
In the aforementioned Patent Bulletins, however, the gear case which protrudes outward is attached to the intermediate casing provided between the two tandem type swash plate hydraulic pumps. Moreover, in the aforementioned Patent Bulletins, the hydraulic pump which is additionally provided in the gear case protruding outward is arranged in parallel with the tandem type swash plate hydraulic pump via the gear supported by a bearing or the chain. Since this tandem type hydraulic pump is driven via the gear or a chain, the number of components increases, and the space area and weight correspondingly increase by the gear case protruding outward and the hydraulic pump.
Furthermore, concerning the hydraulic shovel, a super-small slewing vehicle is developed, leading to the realization of the downsizing of the revolving superstructure, and it is demanded that the tendency for the revolving superstructure to be downsized is enhanced, and that a super-small slewing vehicle which has a high work rate and can be used while traffic travels on one side of the road even in the case of a large-sized vehicle capable of performing rapid construction work is developed. Hence, the downsizing of an engine room is required even in the large-sized vehicle, whereby a hydraulic pump whose axial length is short is demanded also in the two tandem type swash plate hydraulic pumps, and in addition to this, a hydraulic pump arrangement structure capable of providing three or more hydraulic pumps structured in small size as required is strongly demanded.